Steve, can't help you with the grab irons question, but the headlights had a single light in the housing. The "running lights" which are correctly termed "class lights" are a bit more complicated, but perhaps I can give you a short explanation.
These lights, both front and rear, could display three different colors, white, green, and red. The lights, when required by the rules, were normally turned on only on the leading end of the lead locomotive in the consist. White indicated an "extra" train (one not on a timetable schedule), green indicated that it was a "regular train", but that another section of the same regular train was following.
The red light was another animal entirely. It would only have been displayed to the front in cases of emergency, but would have more often been used on the rear of a locomotive or consist as marker lights if the locomotives were running as a train without cars (light locomotives).
In all cases corresponding white, green, and red flags would have also been displayed.
Let me give you a little example that might be easier to understand. Let's say they are running Train #73 in two sections, and you leave Lafayette headed for Bloomington with the first section. You would display green lights (and green flags) on the front of the leading unit which indicates there's another section following.
You get to Bloomington and they need the engine consist back to Lafayette asap, so they run you back north as an extra. You would display white lights to the front on the leading unit (which was the trailing unit going south), and since you have no cars or caboose, you would display the red lights on the rear of the rear unit to act as marker lights.
Regularly scheduled trains, of course, did not display any class lights to the front or rear during normal train operations. / Ron
PS, I would also suggest you consider getting a copy of the Profiles & Station Names CD sold by our Stores Dept. which contains the last version of the Monon Operating Rule book. It is a wealth of good information about prototype operations.